New York City has enacted a tough new policy that allows the authorities to remove newborns from their parents' homes in all but an "extraordinary instance" if the parents previously had children taken from their custody and their case is still open.

John B. Mattingly, the city's commissioner of children's services, announced the more aggressive approach during a City Council budget hearing on Tuesday at which he faced questions on his agency's role in the death of Pablo Paez, an 11–week–old boy whose older sibling had been removed from the same home at age 3 months, a year earlier.

The children's mother, Kiana Paez, a 23-year-old drug addict, was charged on April 25 with beating Pablo to death. Child welfare workers had been in frequent contact with Ms. Paez since the first baby was placed in foster care because of violence in the home, but they did not try to remove Pablo.

Mr. Mattingly said that the new policy was influenced by the Paez case, but that he had been considering the changes — a natural outgrowth of other changes he had made at the agency — for a long time. The policy, which had been toughened in 2006, was officially revised again on April 21, 18 days after the baby's injuries were discovered.

"When I got here three and a half years ago, the assumption was the child would stay in the home," Mr. Mattingly said in a telephone interview. "Most of us in the country have the view that if older siblings are in foster care, and the court has affirmed that they are at substantial risk of harm, it makes very little sense to make the opposite assumption about a 6–pound baby coming into the home."

Even under the new policy, removals will not be automatic. When caseworkers learn of a pregnancy, they are required to have a safety conference with family members, lawyers or advocates to evaluate the risk for the new baby. If they feel a new child should stay in the mother's home, a borough supervisor will have to sign off on the decision. Otherwise, the agency will initiate the court proceedings required to remove any child from the parents' care.

"The assumption should be we are going for removal," Mr. Mattingly said. "This is a very serious matter, and only the highest authority can make a decision not to remove the child."

City officials could not say whether any babies have been removed under the new regulations, but they estimated that 150 to 200 infants a year were born into families with children in foster care.

Several child–welfare experts said on Wednesday that New York's new regulations were among the most aggressive they had seen.

"The presumption is toward keeping a baby home unless there is imminent risk," said Anne Marie Lancour, director of state projects at the American Bar Association's Center on Children and the Law.

Richard Wexler, executive director of the Virginia-based National Coalition for Child Protection Reform and a major critic of foster care, said that New York had basically adopted "a de facto confiscation–at–birth policy."

"What this policy is really saying, to the worker, the supervisor and even the borough commissioner, is, 'Go ahead and leave that child in the home if you want, but if anything goes wrong, your career is over,' " Mr. Wexler said.

For the authorities to remove a child from a home for any significant period of time, they must have an order from a family court judge. Child–welfare officials in New York have long held that a court order for the removal of a single child from a home includes the right to monitor the safety of any new children born into that family. The degree of aggressiveness in how the city pursues that jurisdiction, however, has varied widely over time.

Mr. Mattingly said he had seen a need to tighten the protocols for dealing with such families after reviewing child deaths and seeing too many situations like the one involving Pablo Paez. He declined to state which cases in particular had worried him, but it was clear from his City Council testimony that Pablo's case bothered him deeply.

Officials said that caseworkers had been monitoring the home of Kiana Paez carefully since her first child's placement in foster care, and that her drug screening tests had all come back negative, leading them to believe she was becoming more responsible.

But the Queens district attorney, Richard A. Brown, has said that as a result of abuse at her hands, Pablo had severe brain injury and fractures, including broken ribs and a broken leg.

Bill de Blasio, the chairman of the City Council's General Welfare Committee, praised the new regulations, saying they were "desperately needed." But some parent advocates worried that the aggressive approach might cross a civil rights boundary.

"The extraordinary circumstances language is troubling," said Michael Arsham, executive director of the Child Welfare Organizing Project. "There has to be a reason beyond simply their history. There has to be a new allegation. There has to be an immediate and pressing concern."

Bill Baccaglini, executive director of New York Foundling, one of several dozen foster–care agencies that will help administer the new policy, said he was "willing to be the subject of a little criticism from the civil libertarians."

"This comes out of the best of intentions," he said. "Being on this side of the business I know if we make a mistake you could lose a life."